The present invention relates to a semiconductor having a coupled quantum box array structure to suppress optical phonon scattering by incorporating an artificial structure in a semiconductor.
The electrons in a semiconductor material contribute to electric conduction and are utilized in transistors, for example. The electrons are scattered in a disturbed portion of the crystal and frequently change their directions. Therefore, when an electric field F is applied, the velocity v of the electron flow is not increased simply with the time elapsed, but it flows at a constant velocity determined by .mu..times.F. Here, .mu. is a physical quantity called the electron mobility and is proportional to a mean time interval T of the scattering.
FIG. 1 shows the dependency of electron mobility on temperature in the case of an n-type AlGaAs/GaAs hetero junction. As shown in FIG. 1 (See Physical Review, B condensed Matter, Volume 33, Third Series, Number 12-I, p. 82-97, FIG. 5.), the electron mobility .mu. rapidly decreases when temperature rises, and the decrease becomes very conspicuous when its temperature increases to 100.degree. K. or more. Namely, when the temperature including room temperature exceeds 100.degree. K., thermal vibration (called phonon or lattice vibration) occurs, in which the crystal lattice of the atom groups constituting the crystal lattice is vibrated, whereas it is known that the main cause of the above scattering is the slight disturbance of the lattice arrays caused by thermal vibration. The electron mobility is determined by this thermal vibration.
Particularly, in a polar semiconductor such as GaAs, a lattice vibration called optical phonon controls the scattering, and this determines the characteristics of semiconductor devices such as FETs.
In the past, it has been believed that the dependency of electric resistance on the temperature in semiconductors or metal was caused by the influence of the lattice vibrations on the electrons and that it is unavoidable for the electrons to be placed under the influence of lattice vibration. Accordingly, it is considered essential to cool the semiconductor in order to eliminate the scattering, and the decline of the undesirable electrical characteristics in a semiconductor material due to a temperature rise of the semiconductor material could be suppressed by cooling.